| China is the biggest non-wood pulping country in the world. Wheat straw is the main material in Chinese non-wood pulping industry. The wastewater from straw pulping is difficult to be treated and could pollute the environment if direct discharging. The high concentration of organics and the low degradability of lignin in the wastewater are the main factors for wastewater treatment in pulping and paper industry. In this study, a soil incubation, a pot experiment and a field trial was carried out to determine the effect of two kinds of lignin, one was from ammonium sulfide pulping process(ammonium sulfide lignin, ASL) and another was from Kraft pulping process(black liquid lignin, BLL), on transformation and effectiveness of soil nitrogen (N) after urea added. The study was aimed to assess the feasibility of land use of lignin and its effects on soil N. The results were showed as following:1. Lignin could decline the soil urease activity. The inhibition of urea hydrolysis was enhanced with increased amount of lignin added. The depression of soil urease activity could exist up to 21 days after lignin addition and the strongest inhibiting effect appeared at the 8th day after addition.Lignin delayed urea hydrolysis by inhibiting urease activity. The release rate of NH4+-N was lenitive. Under the same amount of urea-N condition, the inhibition of urea hydrolysis was sustained up to 3 days with 0.3~0.6 g/kg lignin addition and up to 7 days with lignin addition of 2.7~6.7 g/kg. The lignin also inhibited the conversion of NH4+-N to NO3--N at the same time, which lowered the soil NO3--N content and helped hold N in the form of NH4+-N in soil.2. Compared with no-lignin application treatment, lignin could decrease the content of inorganic N in the soil during the regreening stage of winter wheat. The content of inorganic N in the soil applied with lignin was high during jointing stage of winter wheat. The pattern of soil inorganic N content after lignin application could benefit the N uptake and improve the soil N supplying for winter wheat during the rapid growing stages.When the rate of lignin were at 6000 kg/hm2, the soil inorganic N content was lower until ripening stage compared with non-lignin treatment. The excessive application of any kind of lignin could decrease the content of inorganic N in soil, which might restrict the N uptake and decrease biomass of winter wheat.3. ASL significantly increased the biomass of winter wheat. The yields of straw and grain with ASL increased by 17% compared with non-lignin application. Effects of ASL application were superior to BLL. Lignin application could promote N uptake of plant and increase N agronomic efficiency, apparent N recovery efficiency and partial factor productivity of N fertilizer correspondingly.The yields and beneficial effects were not significant with higher lignin application rates. The study revealed that the optimum rate of ASL and BLL should be at 3200 kg/hm2 and 2800 kg/hm2 respectively.In regards of soil N transformation, crop N uptake and yield, appropriate soil application of lignin could delay the urea hydrolysis and release rate of inorganic N in soil and increase the N uptake and yield of winter wheat. Agricultural application of industrial lignin should be one of meaningful approaches although more studies on soil fertility and crop production with the lignin application are needed. |
